When external forces are applied to a stationary object, stress and strain in that object result. In general, stress is the internal resistance force of the object, while strain is the displacement and deformation that result. More specifically, strain is defined as the amount of deformation per unit length of an object when a load is applied. It can be calculated by dividing the total deformation of the original length by the original length of the object.
Over time, many devices have been devised to measure strain which itself can be either compressive or tensile. One simple type of strain gauge detects a change in an electrical characteristic of the object placed under strain be it in the form of capacitance, inductance, or resistance. If the strain of a particular composition is to be measured, the strain gauge itself is typically mounted to the material by epoxy bonding techniques or the like. Accordingly, when forces applied to the material are to be measured, a resulting strain is necessarily transmitted to the strain gauge and thus any change in its electrical characteristic will in turn be usable in determining the strain of the material being measured.
In one particular area of current interest, the properties of biological articular cartilage need to be measured. This is particularly beneficial in research being conducted with respect to osteoarthritis, since if the characteristics of the cartilage and its interaction with the lubrication provided by the human body, can be determined, advances in medical technology such as treatments for osteoarthritis can be made. Research has shown that the articular cartilage is naturally lubricated through a protein found in synovial fluid called lubricin. Further research may show the serviceable life for the cartilage may be increased if the protein structure can be modified or altered with synthetic agents. However, a difficulty encountered with measuring such materials and thus being able to accurately test agents and lubricants is that their coefficients of function are so small, current measurement technology is insufficient. In addition, such materials have extreme aspect ratios and typically exhibit highly anisotropic characteristics.
In light of the foregoing, a need exists for a newly developed load cell able to measure loads in both a normal and shearing direction, to eliminate the torsional effects of the measuring beam on the data, to provide a rotationless mounting system for the beam, and to concentrate the stress for the biaxial measurements such that measurements of extremely low loads can be detected.